Effects of selenium supply and dietary restriction on maternal and fetal metabolic hormones in pregnant ewe lambs

The objective of these studies was to evaluate the effects of dietary restriction and Se on maternal and fetal metabolic hormones. In Exp. 1, pregnant ewe lambs (n = 32; BW = 45.6 +/- 2.3 kg) were allotted randomly to 1 of 4 treatments. Diets contained (DM basis) either no added Se ( control), or supranutritional Se added as high-Se wheat at 3.0 mg/kg (Sewheat), or sodium selenate at 3 (Se3) and 15 (Se15) mg/kg of Se. Diets ( DM basis) were similar in CP (15.5%) and ME (2.68 Mcal/kg). Treatments were initiated at 50 +/- 5 d of gestation. The control, Se-wheat, Se3, and Se15 treatments provided 2.5, 75, 75, and 375 mu g/kg of BW of Se, respectively. Ewe jugular blood samples were collected at 50, 64, 78, 92, 106, 120, and 134 d of gestation. Fetal serum samples were collected at necropsy on d 134. In Exp. 2, pregnant ewe lambs ( n = 36; BW 53.8 +/- 1.3 kg) were allotted randomly to treatments in a 2 x 2 factorial arrangement. Factors were nutrition ( control, 100% of requirements vs. restricted nutrition, 60% of control) and dietary Se ( adequate Se, 6 mu g/kg of BW vs. high Se, 80 mu g/kg of BW). Selenium treatments were initiated 21 d before breeding, and nutritional treatments were initiated on d 64 of gestation. Diets were 16% CP and 2.12 Mcal/kg of ME ( DM basis). Blood samples were collected from the ewes at 62, 76, 90, 104, 118, 132, and 135 d of gestation. Fetal blood was collected at necropsy on d 135. In Exp. 1, dietary Se source and concentration had no effect ( P > 0.17) on maternal and fetal serum IGF-I, triiodothyronine (T3), or thyroxine (T4) concentrations. Selenium supplementation increased ( P = 0.06) the T4: T3 ratio vs. controls. In Exp. 2, dietary Se had no impact ( P > 0.33) on main effect means for maternal and fetal serum IGF-I, T3, or T4 concentrations from d 62 to 132; however, at d 135, high-Se ewes had lower ( P = 0.01) serum T4 concentrations than adequate- Se ewes. Anutrition by Se interaction ( P = 0.06) was detected for the T4: T3 ratios; ewes fed restricted and adequate- Se diets had greater ( P = 0.10) T4: T3 ratios compared with the other treatments. Nutrient-restricted ewes had lower ( P < 0.05) serum IGF- I, T3, and T4 concentrations. Fetal serum IGF- I concentrations were lower ( P = 0.01) in restricted-vs. control-fed ewes; however, fetal T3 and T4 concentrations were unaffected ( P > 0.13) by dietary Se or maternal plane of nutrition. These data indicate that dietary Se may alter maternal T4: T3 ratios. In addition, nutrient restriction during gestation reduces maternal IGFI, T3, and T4 and fetal IGF-I concentrations.